Single Pd atomic catalyst on Mo2CO2 monolayer (MXene): unusual activity for CO oxidation by trimolecular Eley-Rideal mechanism

The geometric stability, electronic structure and catalytic properties of a single Pd atom deposited on a pristine Mo2CO2 monolayer and a defective Mo2CO2 monolayer with an oxygen vacancy (denoted as Pd/O-V-Mo2CO2) are systematically investigated through density functional theory. We find that the oxygen vacancy (O-V) can stabilize the single Pd atom and make the Pd/O-V-Mo2CO2 system an excellent mono-dispersed atomic catalyst. The Pd dopant serves as an active center which makes the intermediates react productively around it. Three reaction mechanisms are considered for CO oxidation to test the catalytic activity of Pd/O-V-Mo2CO2, which exhibits high activity for CO oxidation via a tri-molecular Eley-Rideal (TER) mechanism with a rate-limiting energy barrier of 0.49 eV. The pre-adsorbed CO molecules on the Pd dopant could transfer electrons to the O-2-2 pi* orbitals, which would promote O-2 molecule activation and induce O-O bond scission. This work demonstrates that the defective monolayer MXene may serve as a promising sort of support to fabricate single atomic catalysts (SACs) for CO oxidation or other reactions, agreeing well with the experimental reports, which opens up a new avenue for the design and fabrication of SACs of MXene-based materials.